A typical oil well structure includes a wellhead, to which are attached the various casings and the tubing through which the oil flows. A structure known as a "Christmas tree" is mounted above the wellhead. It provides various gauges and valves, including those through which the flow of oil is directed.
Blowouts and burning oil wells are a serious environmental hazard and a waste of oil, a limited energy source. Traditionally, oil well fires are extinguished by holding a chimney or flare stack and explosives on top of the wellhead. The chimney and explosives are carried at the end of a long boom on a crane. The explosives are remotely detonated, causing an explosion which extinguishes the fire by depriving it of oxygen. The chimney is removed and a new Christmas tree is placed on the wellhead to stop the uncontrolled release of oil.
The vicinity of a burning oil well is extremely hot and frequently cluttered with debris, particularly if the well head was blown up by explosives or otherwise damaged, as happened to oil wells in Kuwait during the Gulf War. Before the fire can be extinguished using the explosive method, the area must be cleaned of debris, using bulldozers, explosives, or large fans. This process is dangerous and requires fire fighters to approach the burning well fairly closely. To let the fire fighters to get close enough to the wells to work on them, the area must be cooled with water. Frequently, the water must be brought to the site in tankers and sprayed onto the area. Large quantities of water are used.
Even when the fire is finally extinguished, oil still flows from the well, particularly from a well under pressure. The well must be recapped with a new, precisely machined Christmas tree. If the wellhead has been damaged, it must be repaired first. Only when the Christmas tree is in place may its valves be closed, stopping the flow of oil.
Another known method for extinguishing a fire is the injection of a drilling mud/water mixture into the well to block it. This method may also be employed if the explosion failed to extinguish the fire. Afterward, the well must be cleaned out before it can become operational.
A new Christmas tree generally must be attached at a clean, intact flange. If the casing has been damaged, it must be repaired or replaced before a new Christmas tree can be attached.
A further method for extinguishing a burning well uses thermite welding to attach a pipe over the wellhead. Thermite welding is a known welding technique which utilizes the reduction of a metal oxide with aluminum, known as a Goldschmidt reaction. In the thermite welding reaction, iron oxide and aluminum in powdered form are mixed. To initiate the reaction, this composition is heated to ignite the powder. The products react to form aluminum oxide and iron. The heat produced by this reaction is sufficient to melt the resultant products. The molten iron is then used as a filler metal in a weld.
In using thermite welding to extinguish a wellhead fire, a pipe is placed over the wellhead. A thermite charge is placed directly at the location where the weld is desired, such as in the interior of the pipe adjacent the wellhead. The thermite composition is ignited and produces molten metal. The pipe functions as a chimney for the fire, and a valve, previously disposed in the pipe, is used to close off the flow of oil. This method extinguishes the fire, by depriving it of fuel, and caps the flow of oil in a single step. However, in this method, the pipe must be placed on the ground and attached to the wellhead with a member such as a ring, which renders it difficult to fit over most actual wellheads. Also, the molten metal tends not to fill the area between the wellhead and pipe uniformly and the slag is not eliminated from the molten metal, resulting in a weaker weld. Further, the parts to be welded cannot be preheated, which is desirable for a strong bond between the existing parts and the filler metal.